Stats Exam 1 (Chapter 2: Frequency Distributions)

Raw scores

data not yet transformed/analyzed

Frequency distribution

describes pattern of data set

Frequency table

a visual depiction of data that shows how often each value occurred

Outlier

extreme score

Steps for frequency table

1. find highest & lowest score 

2. create 2 columns; label 1st w variable, 2nd as “frequency”

3. list full range of values 

4. count # of scores at each value 

To find percentage

1. divide specific number by total number

2. multiply by 100

Grouped frequency table

allows researcher to depict data visually by writing frequencies within a given interval rather than for a specific value

Steps to make grouped freq. table

1. find highest & lowest scores

2. get full range of data 

3. for decimals, round to nearest whole

4. find best interval size (b/w 5 & 10)

tip: divide range by # of intervals we want, then round to nearest whole 

5. list intervals from highest - lowest 

Histogram

a graph that appears like bar graph but depicts just one variable

• usually based on continuous data

• x-axis = values

• y-axis = frequency

Bar graphs vs. Histograms

bar graphs = good for discrete/nominal data

histograms = good for continuous

Steps to make histogram

1. x-axis = variable, list full range of values (include 0 !!!)

2. y-axis = frequency, list full range of frequencies (include 0 !!)

3. draw bar for each value

4. determine midpoint

Normal Distribution

bell-shaped curve, symmetric, unimodal

Skewed Distributions

one of the tails is pulled away from the center

Positively skewed

tail of distribution extends to the right in a positive direction

• can occur from floor effect: when a constraint prevents variables from taking values below a certain point

Negatively skewed

tail extends to the left in a negative direction

• can be result of ceiling effect: constraint prevents variable from taking values above a given number